The present invention deals with a method for reprocessing scrap rubber where the scrap rubber contains sulphur and is comminuted, and the reclaimed rubber is produced from the comminuted scrap rubber by devulcanization.
The invention also deals with an apparatus for performing this method.
Every year several million tons of scrap rubber, especially old automobile tires, are rejected worldwide, which to date have been only insufficiently utilized as a secondary raw material. Due to the small share of rubber returned into the material circulation cycle by different reprocessing variants, for instance recapping of tires, there results a large accumulation of scrap tires in dumps, which require reprocessing. Hitherto, it was assumed that with scrap tires are naturally non-composable waste materials (DE 2638387).
To date the reprocessing of waste tires proceeded along three different process variants.
In the first variant, the scrap tires, after being granulated down to grain sizes of approximately 25 mm, are utilized as an additive for construction of bituminous road cover layers or strengtheners for athletic grounds. For this purpose the rubber granulate is mixed, in a mixer common in road construction, with cement, gravelly sand or sand, water and bonding improvement agents, and is used as a highly elastic intermediate layer, for instance in highway reconstruction or road rail construction (DE 2638387).
A second possibility of utilizing scrap tires as a secondary raw material consists in subjecting the scrap tires to a pyrolysis, in order to thereby obtain pyrolysis oil as initial material for chemical base materials or fuel oils for generation of heat energy and electrical energy from the use of the thermal energy of the incompletely burned gases by directly driving a gas turbine (DE 2724813). For this purpose the scrap tires are undercooled. The undercooled tires are as a rule fed to begin with to a coarse rubber crusher, where only the rubber of the tires is initially crushed in such a way that it can be detached from the bead wires. A twin rotor hammermill is for instance located downstream of the coarse rubber crusher, which knocks the basic components off from the carcass, which thereupon are sorted as to different grain sizes in a screening drum. Thereupon the rubber granulate is separated in magnetic separators and a screening installation from the remaining metal shares and cord fibers (DE 2724813). Subsequently the rubber ingredients are degassed at a temperature of approximately 500.degree. C. The soot or carbon black produced therein can be used either as a product for further processing or as fuel oil. The incompletely burned gas produced as a result of the degassing process is used for directly driving a gas turbine and thus for energy generation.
The third possibility of utilizing scrap tires as secondary raw material consists in replasticizing the finely comminuted rubber granulate, for instance the rubber powder accumulating during the course of recapping old tires preferably in the extruder, and to reuse the granulate up to 20 shares or parts by weight in the tire breaker strip mixture when recapping old tires. Evident disadvantages of this method are the high installation and energy costs of the extruder or analogous installation as well as the use of chemicals, which cause a chain and/or cross-linkage decomposition or degradation and which remain entirely or partially in the replasticate. In addition only a relatively small part of the accumulating mass of scrap tires can be reused through regeneration.